Premium Unleaded 95 vs 98: Is High-Octane Fuel Worth the Extra Price?

Pulling up to the pumps at an Ampol, Shell, or BP, you’ll see Premium 95 and Premium 98 sitting alongside standard unleaded, carrying hefty price tags. Premium 95 typically costs 12c to 16c more than regular 91, while Premium 98 (BP Ultimate, Shell V-Power, Ampol Amplify) commands a 25c to 35c premium. For an average 60-litre fuel tank, opting for 98 adds $15 to $22 to your receipt. Is it worth the money, or are you just buying into high-octane marketing?

1. The Biggest Myth in Motoring: "Higher Octane Equals More Power"

The single most widespread misconception among Australian motorists is that 98 RON fuel contains "more explosive energy" or "more horsepower" per drop than 91 RON. In mechanical terms, that is completely false. A litre of Unleaded 91 and a litre of Premium 98 contain virtually the exact same amount of thermal energy.

What octane actually measures is a fuel’s resistance to detonation (engine knock). Under extreme heat and cylinder pressure, low-octane fuel can ignite spontaneously before the spark plug fires. This uncontrolled explosion—called knocking or pinging—can rattle pistons, destroy head gaskets, and ruin an engine. Higher octane fuel burns in a stable, controlled manner, allowing high-compression or turbocharged engines to run advanced ignition timing safely.

2. What Happens If You Put 98 in a Standard 91 Car?

If you drive a standard naturally aspirated commuter car (like a Toyota Corolla, Hyundai i30, or Mazda 2) where the factory specification calls for 91 RON:

• Your car’s engine compression ratio is modest (typically 10:1 or lower).
• Its ECU (Engine Control Unit) timing map is factory-programmed for 91 RON.
• Putting 98 into the tank will not advance your ignition timing further than factory parameters. You will receive zero horsepower gain and zero noticeable fuel economy improvement. You are simply spending an extra $20 to donate profit margin to the oil company.

3. What Happens If You Put 91 in a 95/98 Required Car?

Now consider the reverse scenario: you drive a European car (Volkswagen Golf, Audi, BMW, Mercedes-Benz) or a turbocharged performance vehicle (Subaru WRX, Ford Ranger Raptor, Toyota GR Yaris) that explicitly specifies "95 RON Minimum" or "98 RON Only".

If you try to save money by putting cheap 91 into this car:

1. As soon as you accelerate hard or climb a highway hill, the fuel will begin to ping under high boost and cylinder pressure.
2. The engine’s acoustic knock sensor will immediately detect this vibration and signal the ECU.
3. To save the engine from self-destruction, the ECU will aggressively retard ignition timing and enrich the air-fuel mixture.
4. The Result: Your car will feel sluggish, throttle response will drop, and your fuel consumption will increase by 8% to 12%. You completely wipe out the 15c saving you thought you made at the pump!

4. How to Read Your Fuel Flap: Three Simple Rules

• "91 RON Unleaded Only / Minimum": Buy regular 91 or E10. Never waste money on 98.
• "95 RON Required / 91 Safe for Emergency": Buy 95 RON as your standard fuel. If unavailable, 91 will get you home safely, but avoid heavy towing or flooring the throttle.
• "98 RON Recommended for Maximum Output": Designed for high-performance turbocharged and supercharged engines. To get the kilowatts and torque you paid for, stick with 98.